Conventionally, there are variously researched and developed electric safety devices of the type comprising a fuse element adapted to break an electric circuit upon passage of an overcurrent in an electrical appliance, and of the heat-sensitive type adapted to break an electric circuit when an electric appliance is overheated to a temperature exceeding a predetermined safe temperature. Such conventional safety device of the respective type has itself excellent safety characteristics. However, perfect safety cannot be provided by a safety device having only a function to break the electric circuit by the fusing of fuse element on passage of an overcurrent, or a function to break the electric circuit by a circuit-breaking conductive member of the heat-sensitive type when the electrical appliance is overheated to a temperature exceeding a predetermined safe temperature. Namely, no matter how excellent the fuse element may be, such safety device cannot fulfil a safety function if the electric appliance is overheated, independently of an overcurrent. On the other hand, no matter how excellent the circuit-breaking conductive member of the heat-sensitive type may be, such safety device cannot fulfil a safety function on passage of an overcurrent independent from overheat. Thus, such conventional safety devices of the respective types cannot disadvantageously prevent damage of electrical appliance and occurrence of fire accident due to overheat or overcurrent.